In vivo evaluation of histopathologic findings of vascular damage after mechanical thrombectomy with the Tromba device in a canine model of cerebral infarction

A novel stent retriever device for in vivo mechanical thrombectomy for acute cerebral infarction has been developed. In this study, we compared the thrombus removal capacity, potential complications, and extent of vessel wall damage of this novel device with those of the Solitaire FR device by performing a histopathologic analysis using an autopsied canine model. Through this experimental evaluation, we aimed to assess the safety and efficacy of the newly developed thrombus removal device for cerebral infarction. Blood clots (autologous thrombus) were injected into 12 canines. Mechanical thrombectomy was performed in six canines using the newly developed Tromba thrombectomy device (experimental group) and in the other six canines using the Solitaire FR thrombectomy device (control group). Angiographic and histopathologic evaluations were performed 1 month after the blood vessels underwent mechanical thrombectomy. In the experimental group, the reperfusion patency was classified as "no narrowing" in five cases and "moderate narrowing (25%-50% stenosis)" in one case. In the control group, the reperfusion patency was classified as "no narrowing" in four cases, "moderate narrowing (25%-50% stenosis)" in one case, and "slight narrowing (less than 25% stenosis)" in one case. In the experimental group, intimal proliferation was observed in only two cases, endothelial loss was observed in two cases, and device-induced medial injury was observed in one case. In the control group, intimal proliferation was observed in two cases, endothelial loss was observed in one case, and thrombosis (fibrin/platelet) was observed in one case. The Tromba thrombectomy device showed no significant difference to the conventional Solitaire device in angiographic and histopathologic evaluations after thrombus removal. The stability and efficiency of the newly developed Tromba device are considered to be high and comparable to those of Solitaire.

TORSIONAL BEHAVIOR OF STENTS: THE ROLE OF LINKER AND STENT TAPERING INVESTIGATED WITH NUMERICAL SIMULATION

The torsional performance is a major mechanical property of stent. A stent with good torsional performance is easy to deform along blood vessels without damaging the vascular wall to avoid in-stent restenosis (ISR). Therefore, this study aimed to study the effect of stent parameters on torsional performance. The effect of stent parameters on torsional performance was studied via finite element method (FEM). The twist metric (TM) and stress distribution of various stents were compared. The TM values of stents with I-, S-, M-, C-, and V-shaped linkers were 0.0190, 0.0191, 0.0184, 0.0141, and 0.0201[Formula: see text][Formula: see text], respectively. In addition, the TM value of the stent increased by 35.85 times when the number of linkers was increased from 2 to 8 and the stent was twisted at the same angular displacement in clockwise direction. The TM value of the stent with 1.13∘ tapering was 0.010 [Formula: see text], which was lower by 47.64% compared with that of cylindrical stent. Compared with the shape of the linker, the number of linkers had a more remarkable effect on torsional performance. Torsional performance was observably enhanced with the decrease in the number of linkers. Among the five stents with different linker shapes, the torsional performance of the stent with C-shaped linker was the best. Besides, the torsional performance of the tapered stent was better than that of the cylindrical stent. Moreover, the torsional performance increased by increasing the stent tapering. This work might provide insights into better stent design and clinical decisions.

A comparative analysis of solvent cast 3D printed carbonyl iron powder reinforced polycaprolactone polymeric stents for intravascular applications

In the present research, the effectiveness of developed methodology based on solvent cast 3D printing technique was investigated by printing the different geometries of the stents. The carbonyl iron powder (CIP) reinforced polycaprolactone (CIPC) was used to print three pre-existing stent designs such as ABBOTT BVS1.1, PALMAZ-SCHATZ, and ART18Z. The physicochemical behavior was analyzed by X-ray diffraction and scanning electron microscopy. The radial compression test, three-point bending test and stent deployment test were carried out to analyze the mechanical behavior. The degradation behavior of the stents was investigated in static as well as dynamic environment. To investigate the hemocompatible and cytocompatible behaviors of the stents, platelet adhesion test, hemolysis test, protein adsorption, in vitro cell viability test, and live/dead cell viability assay were performed. The results revealed that stents had the adequate mechanical properties to perform the necessary functions in the human coronary. The degradation studies showed slower degradation rate in the dynamic environment in comparison to static environment. in vitro biological analysis indicated that the stents represented excellent resistance to thrombosis, hemocompatible functions as well as cytocompatible nature. The results concluded that PALMAZ-SCHATZ stent represented better mechanical properties, cell viability, blood compatibility, and degradation behavior.

Study on the bending behavior of biodegradable metal cerebral vascular stents using finite element analysis

Excellent bending behavior is evaluated as the primary factor during the design of biodegradable metal cerebral vascular stents (BMCVSs), which enables vascular stents to be successfully delivered to the targeted location and avoids unnecessary damage to blood vessels. Unfortunately, this bending behavior has been barely investigated which limits the design of BMCVSs with optimal structures. Herein, six BMCVSs were designed and their bending process were simulated using finite element analysis (FEA). Then, the effects of the stent bridge connection type and structure on the bending behavior were systematically analyzed and an universal mathematical model was further established, in which the influence of the structure parameters of the stent bridge on the flexibility of stents was considered. After that, the bending mechanism of the high-stress zone of the bridge was investigated. Finally, the causes and effects of the self-contacting phenomenon as well as the inner-stent protrusion phenomenon in the bending state were analyzed theoretically, and corresponding solutions were proposed to optimize the design of stents. The numerical results show that the stents with the dislocation-line W-shaped unit have better flexibility than the other stents. The flexibility is positively correlated to the cube of the length of linear part and to the square of the curvature of curved part. The self-contacting phenomenon of the bridge during bending can constrain the formation of inner-stent protrusion, which can eliminate the negative effects of the implanted stents on the hemodynamics in blood vessels. This study is expected to provide practical guidance for the structural design of BMCVSs for clinical applications.

Multi-Objective Optimization Design of Balloon-Expandable Coronary Stent

PURPOSE

Recent studies suggested that suboptimal delivery and longitudinal stent deformation can result in in-stent restenosis. Therefore, the purpose of this paper was to study the effect of stent geometry on stent flexibility and longitudinal stiffness (LS) and optimize the two metrics simultaneously. Then, the reliable and accurate relationships between metrics and design variables were established.

METHODS

A multi-objective optimization method based on finite element analysis was proposed for the investigation and improvement of stent flexibility and LS. The relative influences of design variables on the two metrics were evaluated on the basis of the main effects. Three surrogate models, namely, the response surface model (RSM), radial basis function neural network (RBF), and Kriging were employed and compared.

RESULTS

The accuracies of the three models in fitting flexibility were nearly similar, although Kriging made more accurate prediction in LS. The link width played important roles in flexibility and LS. Although the flexibility of the optimal stent decreased by 13%, the LS increased by 48.3%.

CONCLUSIONS

The obtained results showed that the multi-objective optimization method is efficient in predicting an optimal stent design. The method presented in this paper can be useful in optimizing stent design and improving the comprehensive mechanical properties of stents.